A young dicot stem has a ring of separate vascular bundles…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A young dicot stem has a ring of separate vascular bundles. After some time it has a continuous ring of cambium.
- Name the cambium that is already inside each bundle.
- Where does the second part of the cambium form, and what is it called?
- How do the two parts together become a ring?
Need a reminder? The key ideaShow
Secondary growth makes dicot stems and roots thicker. It is done by the vascular cambium and the cork cambium. A dicot vascular bundle is open, with fascicular cambium between the xylem and the phloem. Interfascicular cambium forms from cells of the medullary rays, and the two join into a ring. The cambium cuts off secondary xylem inward and secondary phloem outward, and makes much more xylem than phloem. Monocot bundles are closed and have no cambium. In a dicot root the cambium arises from conjunctive tissue and the pericycle.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The strip between the xylem and the phloem is the fascicular cambium.
Step 2. (b) Cells of the medullary rays between the bundles start to divide again. They form the interfascicular cambium.
Step 3. (c) The interfascicular cambium joins the fascicular cambium of the neighbouring bundles on both sides. The strips form one continuous ring of vascular cambium round the pith.
Answer: (a) fascicular; (b) in the medullary rays, interfascicular; (c) the strips join into a ring.
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